1. Field of the Invention
The present invention relates to a semiconductor fabrication system and to a method of operating the same, and more particularly, the present invention relates to a lithography system which has a mechanism for setting optimal process parameters and to a method of operating the same.
2. Description of the Related Art
As the integration level of semiconductor devices increases, high precision and optimal performance capabilities become more important in the fabrication of such devices. In particular, a lithography process which is used to form a fine pattern on a semiconductor substrate has become especially important. In order to obtain ultra fine and ultra dense patterns, a 248 nm-wavelength optical source is used as the optical source in current lithography systems, as opposed to the more conventional 365 nm-wavelength optical source. However, the use of such a short wavelength optical source is often accompanied by a degraded reliability of the lithography process.
Generally, a lithography system includes a spinner and a stepper. The spinner includes a coating unit for coating a mask film, that is, a photoresist film, on a semiconductor substrate, a baking unit for baking the coating of photoresist film, a cooling unit for reducing the temperature of the photoresist film, and a developing unit for developing the photoresist film. The stepper performs an exposure process using light having a predetermined wavelength. The process parameters for the stepper and each of the unit devices in the spinner are determined by controllers connected thereto. The controllers only output simple information such as the point in time when a semiconductor wafer is loaded into a lithography system, and uniformly determine the process parameters for the stepper and each of the unit devices in the spinner. That is, a uniform process parameter is applied regardless of the characteristics of each semiconductor wafer, which increases the probability that failure may occur in the processing of each unit.
For example, in conventional systems, a uniform process parameter may be applied to each unit of the spinner despite the fact that optimum time and temperature parameters for a baking process can vary with a stacked structure, and as a result errors can be generated in the process.
An object of the present invention is to provide a lithography system which includes a mechanism for setting an optimal process parameter according to a previous process applied to each semiconductor wafer.
Another object of the present invention is to provide a method of operating a lithography system by setting an optimal process parameter according to a previous process applied to each semiconductor wafer.
To achieve the first object, the present invention provides a lithography system including a spinner, a first controller, a stepper and a second controller. The spinner coats a photoresist film on a semiconductor substrate. When the wafer is loaded into the spinner, the first controller sets a first optimal process parameter according to external information denoting characteristics of the semiconductor wafer and controls the spinner according to the first optimal process parameter. The stepper exposes the semiconductor wafer, which is coated with a photoresist film, to light of a predetermined wavelength. When the semiconductor wafer coated with the photoresist film is loaded into the stepper, the second controller sets a second optimal process parameter according to the external information denoting characteristics of the semiconductor wafer and controls the stepper according to the second optimal process parameter.
Preferably, each of the first and second controllers includes a wafer information reading unit for receiving and reading the external information denoting characteristics of the semiconductor wafer from a database, an optimal process parameter setting unit for determining an optimal process parameter by comparing and matching data of a pre-stored optimal process parameter table to information read by the wafer information reading unit; and a control command generation unit for generating a control command to perform a process in accordance with the optimal process parameter determined by the optimal process parameter setting unit.
The spinner can include a baking unit for baking the photoresist film to cure the same, and a cooling unit for cooling the photoresist film. In this case, the process parameter, which is set by the first controller, includes a baking temperature and a baking time for the baking unit, and a cooling temperature and a cooling time for the cooling unit.
The spinner can further include a developing unit for removing a portion of the photoresist film from the semiconductor wafer which has been exposed by the stepper. In this case, the process parameter, which is set by the first controller, also includes a developing time for the developing unit.
The process parameter which is set by the second controller may include an exposure time, a focus setting, a number of images, and an overlay correction value for the stepper.
To achieve the second object, the present invention provides a method of operating a lithography system which includes a spinner for coating, baking, cooling and developing a photoresist film, a stepper for exposing the photoresist film, and first and second controllers for respectively controlling the spinner and the stepper. In the method, first wafer information is applied to the first controller when a semiconductor wafer is loaded on a transfer unit within the spinner. A first optimal process parameter is set within the spinner according to the received first wafer information. Coating, baking and cooling the photoresist film are performed within the spinner in accordance with the first process parameter. Second wafer information is applied to the second controller when the semiconductor wafer is loaded into the stepper. A second optimal process parameter is set within the stepper according to the received second wafer information. The photoresist film is exposed to light within the stepper in accordance with the second process parameter. Third wafer information is applied to the first controller when the semiconductor wafer, which has been subjected to the exposure process, is reloaded into the spinner. A third optimal process parameter is set within the spinner according to the received third wafer information. The photoresist film is developed within the spinner in accordance with the third process parameter.
Here, the first process parameter can include a baking temperature and baking time for the baking within spinner, and a cooling temperature and a cooling time for the cooling within the spinner. The second process parameter can include an exposure time, a focus setting, a number of images, and an overlay correction value for the stepper. The third process parameter can include a developing time for the developing process in the spinner.
In accordance with the lithography system and the operating method thereof of the present invention, the first and second controllers, which respectively control the spinner and the stepper of the lithography system, determine optimal process parameters that are the most suitable for each semiconductor wafer according to received wafer information. Also, the controllers control the spinner and the stepper so that a process is realized in accordance with the process parameters, whereby a lithography process can be optimally performed.